This invention relates to tone signals, and particularly to the detection of certain tone signals.
In communication systems, voice band signals or tones are used to transmit data or supervisory information, for example, TOUCH-TONE, audible ring, busy, etc. Tone signals may comprise either single tones or mutliple tones. Prior tone detectors have utilized filter circuits which select the frequency component or components of interest by means of very narrow band pass filters and power measuring circuits to measure the power in the neighborhood of the selected frequency. In such prior art circuits a filter circuit is required for each tone component. This invention, however, can detect signals of either type using a single set of estimator circuits and one or more sets of decision circuits depending on the particular application.
Prior tone detectors indicate the presence of a tone whenever a signal of the desired frequency and power is present, regardless of the rest of the frequency spectrum characteristics and, therefore, often require additional circuitry to avodi generating erroneous outputs. This invention detects the presence of a desired signal based on the characteristics of the entire bandpass spectrum of the detector and, therefore, can reject many erroneous signals without additional circuitry.
This invention may be advantageously implemented using large scale integration since no inductors are required for either an analog or digital implementation.